The present invention relates to cathodes for lasers, and has particular relation to such cathodes with extended life.
A typical cathode for a laser, especially a laser in a ring laser gyro (RLG), is a dome of aluminum sealed to a glass-ceramic body. It is desirable for the RLG, and thus for the cathode, to be as small as possible, since many military and commerical applications require instruments to fit into a predescribed volume. At the same time, small cathodes imply high current densities, which imply reduced life spans. One important mechanism in cathode failure is sputter entrapment of the lasing gas. As ions from the lasing gas strike the cathode, aluminum ions are sputtered from the cathode and are reattracted to the cathode, and/or to the surface under the cathode. As they fall back upon the cathode or upon the surface under the cathode, they entrap molecules of the lasing gas, thereby removing such lasing gas molecules from operation. Eventually there is insufficient lasing gas for lasing to continue, and the apparatus fails.
One means of extending cathode life has been to oxidize the inner surface of the cathode with a thin layer of aluminum oxide. The aluminum oxide is more resistant to being sputtered than is the underlying aluminum itself. Even with this improvement, however, current density must be kept below some maximum, or the ions from the lasing gas (typically neon) will strike with sufficient force to sputter the aluminum oxide layer and eventually to sputter the underlying aluminum also, with the aforementioned deleterious results.